Coupling light into (and/or out of) an optical waveguide is a key requirement for any optical or opto-electronic integrated circuit arrangement. Several approaches commonly used in the art include, for example, grating couplers, prism couplers and “end-fire” couplers (i.e., coupling into an optical facet along an endface of an optical substrate). End-fire coupling, for example, into a nanotaper structure formed on an optical substrate offers advantages of simplicity, wide bandwidth of operation and (potentially) polarization independent operation. See, for example, an article entitled “Nanotaper for compact mode conversion” by V. R. Almeida et al., appearing in Optics Letters, Vol. 28, No. 15, Aug. 1, 2003.
One remaining difficulty with end-fire coupling, however, is the need for facet preparation of the waveguide at the endface of the optical substrate. In order to maximize coupling efficiency between a free space signal and the waveguide, the endface facet of the waveguide substrate should be as smooth as possible (i.e., “optically smooth”) so as to limit the effects of scattering and reflections. In most conventional systems, optical polishing and/or cleaving operations are used to create the waveguide endface facet. Facet polishing, however, is a time consuming process that is not considered to be readily compatible with low-cost, wafer-scale production. The cleaving process has its own limitations, primarily associated with cleaving a crystalline material with the crystal cleavage planes required for the input/output coupling locations.
Thus, a need remains in the art for providing optically smooth coupling facets in a manner that is compatible with low-cost, wafer-scale production.